This invention concerns screens of the type disclosed in UK Patent Specification GB 2,322,590 and GB 2,292,533 and to a method and device for joining such screens end to end.
Screens of the type described such as shown in GB 2,322,590 and GB 2,292,533, have been provided with male and female edge formations at the ends of the screen frames, for the purpose of sealing the joint and to accommodate angular orientation of one screen relative to another when fitted within a shaker or sifting machine. However, none of the joints reliably connect one screen to the other to enable the two screens to be handled as one, when joined together and located in a frame support structure of such a machine.
It is an object of the present invention to provide for such a connection between the front edge of a rear screen and the rear edge of a front screen when mounted one behind the other in a shaker or sifting machine.
According to the present invention there is provided a screen of the type described wherein one end of the screen frame is provided with an upwardly open channel profile and the other end with a similar but downwardly open channel profile, such that the outboard edge of an upwardly open profile will fit within the channel of a downwardly open profile provided along the edge of an adjoining screen frame, to enable two such screens to be connected together and to enable linear movement in a direction generally perpendicular to the line of engagement and generally in the plane of at least one of the two screens, to be transmitted from one screen frame to the other.
The invention also lies in a screen as aforesaid when fitted to an adjoining similar screen wherein the engagement of one profile by another also serves to close the gap between the two screen frames and prevent at least particulate material from passing therebetween.
Preferably the engagement of the two profiles is adapted to prevent liquid from passing therebetween.
Typically when fitted in a support structure in a shaker or sifting machine a screen as aforesaid, together with a second similar screen, are arranged in tandem, one behind the other, the inner one constituting the rear screen and the other the front screen of a pair when viewed from the front of the machine.
In such an arrangement the two screens may be in generally planar alignment.
When combined to form a pair of screens the engagement may comprise a lost motion connection so as to permit one frame to be hingeable relative to the other about the connection.
In some applications the support structure may be adapted so as to cause one screen to be angled relative to the plane of the other.
Whether aligned in one plane or angled, the engagement of the two frame edge profiles provides a reliable force-transmitting connection to enable a rear screen frame to be removed from the support structure simply by pulling out the front frame of the pair.
A support structure for such a pair of screens typically comprises parallel rails for supporting left and right hand edges of the two screen frames, a transversely extending rear ledge for supporting the far end of the rear screen frame, and an inflatable rim seal which when inflated and pressurised firmly sandwiches the edges of the frames between the inflated seal and the rails and the ledge so as to prevent any movement of the frames in the support structure once the seal is inflated, but which when deflated permits movement of the screens relative to the rails for movement in and out of the support structure and also vertical movement of one frame relative to the other, to facilitate the entry of one profile into the other to effect the said engagement with the two screens in the support structure and the invention lies in a support structure as aforesaid when fitted with two such screens.
The invention also lies in method of joining two screens as aforesaid in a support structure which comprises parallel rails for supporting left and right hand edges of the two screen frames and a transversely extending rear ledge for supporting the far end of the rear screen frame, and an inflatable rim seal which when inflated and pressurised firmly sandwiches the edges of the frames between the inflated seal and the rails and the ledge so as to prevent any movement of the frames in the support structure once the seal is inflated, but which when deflated permits movement of the screens relative to the rails for movement in and out of the support structure and also vertical movement of one frame relative to the other, wherein the end of the frame provided with the downwardly open profile is lifted up within the support structure relative to the upwardly open profile provided at the end of the other frame, to allow the downwardly open profile to pass up and over the outboard wall of the channel of the upwardly open profile and thereafter to drop into and engage the said channel to effect the engagement.
The two screens may be slid one after the other into the support structure with the first to be slid into position being arranged with its upwardly open profile at its trailing end.
Preferably the second screen to be pushed into the support structure is inserted until its leading end abuts the rear end of the first screen, and the external shape of the profiles is adapted to cause the leading end of the second screen to rise up and over the profile on the rear end of the first screen with continued forward movement of the second screen.
Two screens which have been fitted in a support structure aforesaid may be removed therefrom by deflating the rim seal, pulling the two frames out as one until the first frame is clear of the support structure, disengaging the edge profile of its inboard end from the edge profile along the outboard edge of the inner screen, and thereafter gripping the latter, and pulling it in an outward sense until it also is clear of the support structure.
Although the male/female engagement of the edges of the frames described in GB 2,322,590 and GB 2,292,533 provided a degree of interference as between one frame and the next when in line, the engagement of these frame edges did not provide a reliable force-transmitting connection such as has been found to be necessary to allow a rear frame to be pulled out simply by pulling out the front frame of a pair, especially after use, when both frames are heavily encrusted with mud and especially the rear one may be very resistant to sliding movement.
As stated, the screens may be located in a support structure comprising parallel rails for supporting the left and right hand edges of the frames and a transversely extending rear ledge for supporting the far end of the rear screen frame, and an inflatable rim seal is provided which when pressurised firmly sandwiches the edges of the frames between the inflated seal and the rails and the ledge. Once inflated, the squeeze exerted on the frame edges prevents any movement of the frames. However once deflated, both frames are not only capable of being slid along the rails but are also capable of limited relative vertical movement. It is this latter degree of freedom which renders the engagement shown in the earlier Patent Specifications insufficient to provide a reliable traction connection to be provided between the two frames.
Likewise this relative vertical movement, which is possible when the seal is deflated, may be employed as already described to assist in joining the edges of a pair of screen frames embodying the invention, to permit one frame to be lifted relative to the other to allow its outboard downwardly extending edge profile lip to be lifted over the corresponding but upwardly extending edge profile lip at the adjoining end of the other frame, thereafter to be dropped thereinto to effect the join.
Of course, once the two edges are so engaged, the two frames are positively joined together and sliding movement of one, in a direction perpendicular to the join, will be reliably transmitted to the other, so that the two will move as one. As already described the rear frame therefore can be pulled out simply by pulling the front frame. Once the latter is clear of the support assembly within the chamber, the edge profile of its rear end can be disengaged from the edge profile along the front edge of the rear screen. The latter is then available to be pulled out by gripping it along its front leading edge, and pulling.